Is it correct that you can't see an NPC after you're 3x its level? I was just wondering if I should start being more picky about when I use my T.O. Sentry Bots, now that I'm over level 390.

I don't know about Commons/Uncommons, but I am 340ish and can still see Rank 100 Dark Rings...

For bosses when they are shared you see the max rank, for most it is 3x rank. I've guessed that most other NPC with fixed rank is also limited by 3x rank.

I mean I still see them. I shared a Ring just yesterday. Perhaps Elite/Boss NPCs are visible to the entire established rank range. Dark Rings are 60-450, so I guess anyone in that range would be able to find them as well as see the alert. But again, for Commons/Uncommons I don't know. I guess I'll find out at 360/361 if Replicators go away...

Alright, I can still see Raptors at 421, so I guess it's not true.